docs: def _render_relationships(self, resource):
          """Render the resource's relationships."""
          relationships = {}
          related_models = resource.__mapper__.relationships.keys()
          primary_key_val = getattr(resource, self.primary_key)
          if self.dasherize:
              mapped_relationships = {
                  x: dasherize(underscore(x)) for x in related_models}
          else:
              mapped_relationships = {x: x for x in related_models}
  
          for model in related_models:
              relationships[mapped_relationships[model]] = {
                  'links': {
                      'self': '/{}/{}/relationships/{}'.format(
                          resource.__tablename__,
                          primary_key_val,
                          mapped_relationships[model]),
                      'related': '/{}/{}/{}'.format(
                          resource.__tablename__,
                          primary_key_val,
                          mapped_relationships[model])
                  }
              }
  
          return relationships